Add a linter rule for unary prefix expression spacing

Summary: Add a linter rule to ensure that there is no space between the operator and the operand in a unary prefix expression.

Test Plan: Added test cases.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D13797